Ablation-transfer imaging/recording

ABSTRACT

A unique method/system for simultaneously creating and transferring a contrasting pattern of intelligence on and from an ablation-transfer imaging medium to a receptor element in contiguous registration therewith is not dependent upon contrast imaging materials that must absorb the imaging radiation and is well adopted for such applications as, e.g., color proofing and printing, the security coding of various documents and the production of masks for the graphic arts and printed circuit industries; the ablation-transfer imaging medium, per se, comprises a support substrate and an imaging radiation-, preferably a laser radiation-ablative topcoat essentially coextensive therewith, such ablative topcoat having a non-imaging ablation sensitizer and an imaging amount of a non-ablation sensitizing contrast imaging material contained therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of our now-abandoned application Ser.No. 08/525,039, filed Sep. 8, 1995, which is a continuation of ournow-abandoned application Ser. No. 08/193,767, filed Feb. 9, 1994, whichis a continuation of our now-abandoned application Ser. No. 07/841,488,filed Feb. 26, 1992, which is both a continuation-in-part of ournow-abandoned application Ser. No. 07/592,790, filed Oct. 4, 1990 and adivision of our application Ser. No. 07/706,775, filed May 29, 1991 andnow U.S. Pat. No. 5,156,938, issued Oct. 20, 1992, which applicationSer. No. 07/706,775 is a continuation-in-part of our now-abandonedapplication Ser. No. 07/497,648, filed Mar. 23, 1990, which is in turn acontinuation-in-part of our now-abandoned application Ser. No.07/330,497, filed Mar. 30, 1989. In U.S. Pat. No. 5,171,650, issued Dec.15, 1992 from the application of Ernest W. Ellis, et al., Ser. No.07/707,039, filed of even date with said application Ser. No.07/076,775, are disclosed and claimed a method/system of simultaneouslycreating and transferring a contrasting pattern of intelligence on andfrom a composite ablation-transfer imaging medium to a receptor elementin contiguous registration therewith, the composite ablation-transferimaging medium including at least one intermediate dynamic releaselayer, said application Ser. No. 07/707,039 being a continuation-in-partof commonly-assigned and now-abandoned application Ser. No. 07/592,790,filed Oct. 4, 1990.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to novel ablation-transfer imaging mediacomprising a support substrate having an imaging radiation-ablativetopcoat essentially coextensive therewith, the imagingradiation-ablative topcoat including an ablation sensitizer and animaging amount of a non-ablation sensitizing contrast imaging materialcontained therein. This invention also relates to a transfermethod/system for simultaneously creating and transferring a contrastingpattern of intelligence on and from such ablation-transfer imaging mediato a receptor element in contiguous registration therewith, whereby saidimaging material delineates said pattern of intelligence thereon. Thepattern of intelligence transferred to the receptor element is thus ofopposite sign of that simultaneously created on the imaging medium.

The present invention especially relates to photo-inducedablation-transfer imaging/recording and, preferably, to laser-inducedablation-transfer imaging/recording particularly adopted for suchapplications as color printing/proofing and masking.

2. Description of the Prior Art

The phenomenon of, e.g., laser-induced ablation-transfer imaging, isgenerically known to this art and is believed to entail both complexnon-equilibrium physical and chemical mechanisms. Indeed, suchlaser-induced ablation-transfer is thought to be effected by the rapidand transient accumulation of pressure beneath and/or within a masstransfer layer initiated by imagewise irradiation. Transient pressureaccumulation can be attributed to one or more of the following factors:rapid gas formation via chemical decomposition and/or rapid heating oftrapped gases, evaporation, photo and thermal expansion, ionizationand/or by propagation of a shockwave. The force produced by the releaseof such pressure is preferably sufficient to cause transfer of theimaging layer to an adjacent receptor element. The force is preferablysufficient to effect the complete transfer of the exposed area of anentire layer rather than the partial or selective transfer of componentsthereof.

Other material transfer imaging/recording techniques based onequilibrium physical changes in the material are also known to this art,but are limited in terms of both the overall speed of the process aswell as in the materials which can be employed therefor. In particular,ablation transfer differs from the known material transfer techniquessuch as, for example, thermal melt transfer and dye sublimation/dyediffusion thermal transfer (D2T2). Each of these prior art techniquestypically employs thermal print heads as the source of imaging energy.

Alternatively, it is known to employ laser heating in lieu of thethermal printing head. In these systems, the donor sheet includes amaterial which strongly absorbs at the wavelength of the laser emission.In the thermal melt transfer process, when the donor sheet isirradiated, this absorbing material converts the laser light to thermalenergy and transfers the heat to a colorant transfer layer which alsoincludes a binder, fusible compound, etc., thereby raising itstemperature above its melting point to effect its transfer onto anadjacent receptor sheet. In the D2T2 process, only the colorant istransferred to a specially treated or special receptor sheet (e.g.,coated or porous) by sublimation or thermal diffusion. See, for example,JP 62/140,884, UK Patent Application GB 2,083,726 and U.S. Pat. Nos.4,804,975, 4,804,977, 4,876,235, 4,753,923 and 4,912,083.

Compare also U.S. Pat. No. 3,745,586 relating to the use of laser energyto selectively irradiate the uncoated surface of a thin film element,coated on one side with a contrast imaging absorber, to vaporize and tocause the selective transfer of the absorber coating to an adjacentlyspaced receptor, and U.S. Pat. No. 3,978,247 relating to sublimationtransfer recording via laser energy (laser addressed D2T2), wherein thecontrast imaging material is also the absorber.

Nonetheless, these processes are limited in a variety of significantrespects. For example, in melt transfer, the composition must containlow melting materials to transfer a pigment or dye and receptor sheetsappropriately textured for wicking or having special coatings arerequired for best results. In D2T2, only the imaging dye itself istransferred; thus, it becomes necessary to employ special receptorsheets in order to effectively bind and stabilize (“trap”) the dye.Compare, for example, U.S. Pat. No. 4,914,078 to Hann et al.Furthermore, additional post-heating treatment steps, such as the“setting” of the dyes in the binder which is present on the receptorsheet increases both the complexity and the time associated with theprocess. Such process is also limited to those dyes and pigments whichundergo sublimation or diffusion in response to the particular imagingstimulus.

These processes are further limited in that the relatively slowprocesses of heat diffusion and thermal equilibrium are involved.

Accordingly, need exists in this art for a transfer process which is farmore rapid than current transfer techniques, which can effectivelyemploy a wide variety of contrast materials and which is not limited tospecially treated or special receptor elements.

Laser-induced recording based on the removal or displacement of materialfrom the exposed area is also known to the recording art. However, theseapplications do not require transfer of material from one substrate toanother. Historically, laser-induced recording has been used, forexample, in optical disk writing with near infrared (IR) laserstypically emitting at wavelengths ranging from 760 nm to 850 nm employedas the writing source. Since polymeric binders are typicallynon-absorbent in the near infrared region (760 nm to 2500 nm), infraredabsorbers, i.e., sensitizers, are added to the binders to absorb thelaser radiation. This arrangement allows the laser radiation absorbed bythe sensitizer to be converted to heat which causes pit formation. See,for example, U.S. Pat. Nos. 4,415,621, 4,446,233, 4,582,776 and4,809,022 and N. Shimadzu et al, The Journal of Imaging Technology, Vol.15, No. 1, pg. 19 (1989). However, because this technology does notentail the imagewise transfer of materials from one substrate toanother, these systems will not be further discussed.

There also exist in the recording art instances of laser-inducedablative transfer imaging entailing the displacement of material from adonor medium and adherently transferring same to an adjacent receptorelement. These are limited to the use of large amounts of a black bodyabsorber such as graphite or carbon black in conjunction with a Nd:YAGlaser emitting at 1064 nm to transfer a black image. See, for example,U.S. Pat. Nos. 4,245,003, 4,702,958 and 4,711,834 (graphitesensitizer/absorber), U.S. Pat. No. 4,588,674 (carbon blacksensitizer/absorber), and Great Britain Patent No. 2,176,018A (smallamounts of Cyasorb IR 165, 126 or 99 in combination with graphite as thesensitizer/absorber).

To produce these particular imaging media, the sensitizers/absorbers areusually dispersed in commercially available binders and coated onto alaser transparent support. The binders include both self-oxidizingbinders, e.g., nitrocellulose, as well as non-self oxidizing binderssuch as, for example, ethylcellulose, acrylic resins,polymethylmethacrylate, polystyrene, phenolic resins, polyvinylidenechloride, vinyl chloride/vinyl acetate copolymers, cellulosic esters andthe like. Since the black body absorbers employed are highly absorbentin the visible and ultraviolet (UV) as well as in the infrared region,the resulting transferred image is always black due to the presence ofthe absorber. Such ablative transfer imaging based on black bodyabsorbers is therefore entirely ineffective and wholly unsuited for manyapplications, e.g., color transfer imaging, color proofing, invisiblesecurity printing, etc.

Thus, serious need continues to exist in this art for a photo-inducedablative transfer imaging medium that can be sensitized independently ofthe contrast imaging material(s) and is therefore not limited tocontrast materials which must absorb the imaging radiation. Like needexists for an ablative transfer imaging medium that may be sensitized toabsorb visible and/or near IR light.

In particular, existing desiderata in this art include:

1. Media that can be employed in a photo-induced ablative transferprocess to provide full color images faster than possible using currentmelt or sublimation techniques and that can be tailored to meet a widevariety of specifications for color imaging.

2. Media that can be employed in a photo-induced ablative transferprocess to produce masks which selectively block the light from exposureunits employed in pre-press production in the graphic arts and printedcircuit industries.

3. Media that can be employed in a photo-induced ablative transferprocess to produce substantially colorless fluorescent images, e.g., forthe security marking of documents.

SUMMARY OF THE INVENTION

Accordingly, a major object of the present invention is the provision ofnovel technique for ablation-transfer imaging/recording that is notdependent upon contrast imaging materials that must absorb the imagingradiation and which novel technique otherwise avoids or conspicuouslyameliorates the above disadvantages and drawbacks to date characterizingthe state of this art.

Another object of this invention is the provision of novel technique forablation-transfer imaging/recording that is not dependent upon contrastimaging materials that must absorb the imaging radiation and which iswell adopted, in contradistinction to the known state of the ablativerecording art, for such applications as multi-color/polychromal colorproofing and color printing under a single set of imaging conditions.

Briefly, the present invention features a method for transferring acontrasting pattern of intelligence from an ablation-transfer imagingmedium to a receptor element in contiguous registration therewith, saidablation-transfer imaging medium comprising a support substrate and animaging radiation-ablative topcoat essentially coextensive therewith,especially a photo- and more preferably a laser-ablative topcoat, saidessentially coextensive topcoat comprising an effectiveablative-transfer effecting amount of a non-imaging sensitizer thatabsorbs such imaging radiation, e.g., laser energy, at a rate sufficientto effect the imagewise ablation mass transfer of said topcoat, and saidimaging radiative-ablative topcoat including an imaging amount of anon-ablation sensitizing contrast imaging material contained therein. Inparticular, the present invention features a transfer method comprisingimagewise irradiating said ablation-transfer imaging medium according tosuch pattern of intelligence at a rate sufficient to effect the ablationmass transfer of the imagewise-exposed area of the radiation-ablativetopcoat of said imaging medium securedly onto said receptor element andwhereby said imaging material delineates said pattern of intelligencethereon.

This invention also features such ablation-transfer imaging medium, perse, as well as an organization adopted for ablation-transferimaging/recording including such ablation-transfer imaging medium and areceptor element in contiguous registration therewith, e.g., inface-to-face registered direct contact, or even spaced a slight distancetherefrom which can extend up to 25 and in certain instances even up to100 microns.

The present invention also features an assembly for ablation-transferimaging/recording comprising the aforesaid organization and means forselectively irradiating, e.g., with laser energy or other sources ofelectromagnetic and even ultrasonic radiation, said ablation-transferimaging medium to effect the ablation mass transfer of theselectively-irradiated area of the radiation-ablative topcoat of theimaging medium securedly onto the receptor element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view photomicrograph of an imaging medium according tothe present invention and the illuminated space above same, 100nanoseconds after initiation of a 260 nanosecond laser pulse directedthrough the support substrate of said imaging medium and into theablative topcoat thereof (the photomicrograph shows both the laserexposed and unexposed areas of the imaging medium);

FIG. 2 is a schematic/diagrammatic illustration of the method/systemaccording to the present invention, including one embodiment of theimaging medium wherein the support substrate thereof is transparent tothe imaging radiation; and

FIG. 3 is a schematic/diagrammatic illustration of another method/systemof this invention, including a second embodiment of the imaging mediumwherein the support substrate thereof is not transparent to the imagingradiation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

More particularly according to the present invention, it will beappreciated that the imaging radiation-ablative topcoat necessarilycontains both a non-imaging ablation sensitizer that absorbs the imagingradiation as well as a non-ablation sensitizing contrast imagingmaterial.

It will thus be seen that the ablation-transfer imaging media of thisinvention provide the distinct advantage of being sensitizedindependently of the contrast imaging material, a feature conspicuouslyalien to the prior art.

By “ablation sensitizer” is intended any initiator capable of initiatingand promoting the ablation process. It does this by absorbing theimaging radiation and transferring the absorbed energy into an explosiveablative force. Such sensitizers/initiators are well known to therecording art. Light sensitization for imaging materials is of coursealso well known to the recording art. However, in markedcontradistinction to the aforediscussed prior art laser-induced ablativetransfer imaging (wherein a material is also displaced from a donorsheet and adherently transferred to a receptor element to record apattern of intelligence thereon), the sensitizers of the presentinvention do not serve to distinguish or delineate the pattern ofintelligence. Their intended function is not reading.

For example, in color imaging applications, the sensitizer(s) of theinvention is (are) substantially colorless. For security printingapplications where UV light is used to cause fluorescence of aninvisible pattern of intelligence, the sensitizer(s) of the inventiondoes (do) not fluoresce in the visible region. And for maskingapplications, e.g., for fabricating printed circuits or graphic artspreproduction, the sensitizer(s) of the invention does (do) not functionas the light blocking material.

Accordingly, such non-imaging ablation sensitizer is one that absorbsthe radiation that causes ablation (write mode), but which is invisibleor not substantially discernible to the detector used to distinguish theresulting pattern of contrasting intelligence (read mode). Thesensitizer may be invisible or not discernible because it isnonabsorbing or nonemitting to the detector, or because its absorbanceor emission is below the detection limit. Of course, the sensitizer mustbe capable of effecting the ablation of the topcoat under the intendedimaging conditions when employed without the non-ablation sensitizingcontrast imaging material.

By “non-ablation sensitizing contrast imaging material” is intended thatmaterial used to distinguish or delineate the resulting pattern ofintelligence transferred to the receptor element.

Such contrast imaging material is, furthermore, incapable of initiatingablation-transfer without the above sensitizer/initiator under theintended imaging conditions that result in ablation. Failure of thecontrast imaging material to itself initiate or promote ablation may bethe result of a lack of absorbance at the ablation wavelength(s), a lackof sufficient absorbance of same, or a failure of absorbance to resultin a pressure build up phenomenon, e.g., the absorbance provides anon-ablation promoting event such as photobleaching, stable triplet,fluorescence or phosphorescence. Thus, the contrast imaging materialmust be visible or discernible to the detector/technique used todistinguish the resulting pattern of intelligence transferred to thereceptor element and/or remaining on the imaging medium, per se.

Exemplary such contrast imaging materials that can be ablativelytransferred to a receptor element in a predetermined contrasting patternof intelligence to visibly or symbolically represent or describe anobject or data include the colorants (dyes or pigments), ultraviolet andinfrared absorbing materials, polymeric materials, magnetic materials,fluorescent materials, conducting materials, etc.

In a preferred embodiment of the present invention, the subjectablation-transfer imaging/recording technique is advantageously photo-and more preferably laser-induced.

Photo- or laser-induced ablation-transfer comprehends a threshold energybelow which no effective material transfer occurs and a requirement thatthe energy be input at a rate greater than the ability of the materialsto reverse the factors leading to the aforenoted pressure accumulation,for example by excessive thermal diffusion outside the irradiated area.Thus, imaging radiation capable of exceeding the threshold energy(fluence, joules/cm²) and power density (watts/cm²) is required foreffective image transfer. By proper selection of materials and imagingparameters, this latter requirement can lead to exposure times on ananosecond time scale which is at least ten times faster than exposuretimes necessary for conventional transfer imaging processes. The actualvalues of fluence and power density suitable for photo- andlaser-induced ablative transfer imaging are dependent on the specificmaterials employed in the imaging medium and the specific receptorselected.

In a preferred embodiment of the invention, the imagingradiation-ablative topcoat comprises at least one sensitizer whichabsorbs at the wavelength of the desired laser output in the nearinfrared spectral region of 760 nm to 3,000 nm, and at least oneablative binder. The at least one sensitizer is present in an amountsufficient to effect the rapid partial decomposition of the at least onebinder when the at least one sensitizer interacts with laser light. Theablative binder advantageously comprises those polymeric materials whichundergo rapid acid catalyzed partial decomposition, preferably attemperatures less than 200° C. as measured under equilibrium conditions.The topcoat may also, optionally, contain materials which arenon-absorbing at the wavelength of the desired laser output and/ornon-decomposing, as well as optimal amounts of commercially availablebinders which are not ablative binders in the imaging process. Inanother preferred embodiment, as more fully discussed below, the topcoatcomprises at least one near infrared sensitizer, at least one ablativebinder, and at least one hydrogen atom donating material (H*) for theacid catalyzed decomposition of the ablative binder (which may bepresent in the binder itself).

In another preferred embodiment of the present invention, a nearinfrared laser-ablation transfer imaging medium is provided. Such mediumadvantageously comprises a near infrared transparent support filmbearing a layer of near infrared ablative coating employing asubstantially colorless near infrared sensitizer. This medium can beeffectively and advantageously employed for color imaging when a(non-sensitizing) colorant is added.

Upon exposure to laser light, the absorbing sensitizer interacts withthe laser light and causes rapid partial decomposition of the binder togaseous and non-gaseous products. The rapid expansion of the heatedgases causes ablation of the exposed topcoat onto an adjacent receptorsheet providing a reverse of the imaged color film (i.e., a color printor proof).

Suitable absorbing sensitizers according to the present inventioninclude any material which can absorb at a desired wavelength for aparticular near infrared or visible imaging wavelength and whichpreferably can initiate acid formation upon photo-excitation. Inparticular, where visibly transparent coatings are required, forexample, substituted aromatic diamine dication diradical typesensitizers or cation radical sensitizers with counterions derived fromstrong acids and absorbing in the near IR are preferred. Exemplary suchsensitizers include:

wherein R is alkyl, benzyl, substituted benzyl, etc.; X is SbF₆ ⁻, BF₄⁻, PF₆ ⁻, AsF₆ ⁻, ClO₄ ⁻, B(phenyl)₄ ⁻, triflate and other salts ofstrong acids which are not capable of electron donation to the cationradical or dication radical in the ground state; A is one of theradicals of the formulae:

and B is one of the radicals of the formulae:

in which Y is hydrogen, alkyl, aryl, nitro, halo, benzyl, substitutedbenzyl, etc.

Examples of these sensitizers include the series of near infraredabsorbers marketed under the. trademarks Cyasorb IR 165, 126 and 99 byAmerican Cyanamid, as well as those IR absorbers described in U.S. Pat.No. 4,656,121, hereby expressly incorporated by reference.

Radiation sources emitting near infrared wavelengths in combination withvisibly colorless sensitizers are preferred for high fidelity colorimaging applications. In other applications, any radiation source ofsufficient intensity, typically not less than about 10⁴ watts/cm²,emitting in the visible and/or near infrared can be employed forphoto-ablation without limitation to black body sensitizers asessentially required by the prior art. The sensitizers of the presentinvention are most preferably highly absorbing at the wavelengths of theimaging radiation, soluble in the binders employed, and capable ofinitiating acid formation upon photo-excitation by the imagingradiation. Examples of suitable non-black body sensitizers which can beeffectively employed in the ablative topcoat are cyanine dyes,phthalocyanine dyes, metal dithiolenes, methylene blue salts, di- andtriarylmethane cation salts, Wurster's blue salts, and other visibly ornear infrared absorbing onium salts derived from strong acids, etc.Various of these are described in U.S. Pat. Nos. 4,315,983, 4,508,811,4,948,776, 4,948,777, 4,948,778 and 4,950,640, also hereby expresslyincorporated by reference.

Exemplary radiation emitting devices include solid state lasers,semiconductor diode lasers, gas lasers, xenon lamps, mercury arc lamps,and other visible and near infrared radiation sources which are capableof providing sufficient energy to equal, or exceed, the threshold energyfor ablation transfer and of providing this energy at such a rate as toinstitute that phenomenon of transient pressure accumulation discussedearlier and believed responsible for the ablative transfer process.

Since the value of threshold energy is intensity dependent, as well asmaterials dependent it is desirable to provide this energy as rapidly aspossible. Other constituents on the exposure device include the abilityto be focused to an image spot size and modulated at a dwell timesuitable for the desired application.

Particularly representative devices for providing the imaging radiationinclude lasers such as Nd:YAG lasers emitting at 1064 nm, for examplethat incorporated in the imaging hardware of the Crosfield Datrax 765laser facsimile writer, laser diode systems emitting at 780-840 nm, orother radiation sources designed to provide a power density of 10⁴watts/cm² or greater.

The radiation source is preferably focused to provide the most efficientutilization of energy when it is impinged upon the imaging medium.

The ablative binders according to the present invention areadvantageously those polymeric materials which transfer under theimaging conditions, and are preferably those which undergo rapid acidcatalyzed partial decomposition at temperatures of less than about 200°C. as measured under equilibrium conditions, and most preferably attemperatures of less than about 100° C. as measured under equilibriumconditions.

In particular, the preferred ablative binders according to thisinvention are those binders which decompose rapidly to produce effectiveamounts of gases and volatile fragments at temperatures of less thanabout 200° C. as measured under equilibrium conditions and thedecomposition temperatures of which are significantly reduced in thepresence of small amounts of generated acids. Most preferably, thedecomposition temperatures thereof are decreased to less than about 100°C.

Exemplary such polymers include nitrocellulose, polycarbonates and otherpolymers of the type described in J. M. J. Frechet, F. Bouchard, F. M.

Houlihan, B. Kryczke and E. Eichler, J. Imaging Science; 30(2), pp.59-64 (1986), and related polymers which are hereinafter more fullydiscussed.

Exemplary polycarbonate binders include those of the structure:

wherein B is one of the radicals of the formulae:

or other groups capable of generating a tertiary carbonium ion uponthermolysis and of producing gain or amplification in the decompositionof the polymer by eliminating a proton from the carbonium ion.

Stated differently, in addition to a thermal decomposition, asillustrated in the model system below:

the mechanism of the present invention preferably entails an acidcatalyzed thermal decomposition:

as generally described by J. M. J. Frechet et al, Journal of ImagingScience, 30(2), 59(1986). Commercially available Bisphenol Apolycarbonate decomposes at temperatures greater than 300° C.Non-tertiary diols and polyols may be polymerized in combination withtertiary diols to improve the physical properties of the polymer.

A may be the same as B or selected from among those dihydroxy aromaticor polyhydroxy compounds polymerizable into a polycarbonate.

The compounds:

are preferred.

The synthesis of these polymers has also been described, for example, byJ. M. J. Frechet et al, Polymer Journal, 19(1), pp. 31-49 (1987).

In addition to the polycarbonates, polyurethanes having the followinggeneral structure can also be employed:

wherein B is as defined above and A is selected from among thosearomatic or aliphatic diisocyanates or polyisocyanates copolymerizablewith the above tertiary diols to produce a polyurethane.

The compounds:

are the preferred.

It is known that polyurethanes of primary and secondary diols andpolyols decompose at temperatures greater than about 200° C. by theelimination mechanism:

wherein R is alkyl.

However, polyurethanes containing certain tertiary alcohol recurringstructural units can decompose at temperatures less than about 200° C.by cleavage in a mechanism analogous to that of Frechet'spolycarbonates, as illustrated below:

In addition to the immediately aforesaid polycarbonates, thepolyurethanes that thermally decompose by acid catalysis are alsopreferred.

Small amounts (typically less than 10%) of non-tertiary diols andpolyols may be polymerized in combination with the tertiary diols toimprove the physical properties of such polymer without raising theenergy requirements for ablation-transfer imaging. The synthesis ofthese polyurethanes is described in Example 1 below.

Other than the polycarbonates and polyurethanes, polyesters of thefollowing general formulae derived from malonic or oxalic acid may alsobe employed:

wherein B is as defined above. Polyorthoesters and polyacetals may alsobe used.

Typically, without raising the energy requirements for ablation-transferimaging, small amounts (e.g., less than about 10%) of non-tertiary diolsand polyols may be polymerized in combination with B to improve thephysical properties of the polymer.

Small amounts (e.g., typically less than about 10%) of other compatibledi- and polyacids may be polymerized in combination with the malonic oroxalic acid to improve the physical properties of the polymer withoutraising the energy requirements for ablation-transfer imaging.

Alternating block copolymers containing polycarbonate, polyurethaneand/or polyester recurring structural units as described above, as wellas those including polyorthoester and polyacetal recurring structuralunits, may also be used.

Other suitable ablative binder polymers include nitrocellulose, with alow viscosity SS (solvent soluble) nitrocellulose being particularlypreferred from a coatability standpoint. Other examples ofnitrocellulose which can be employed are described at pages 329-336 ofCellulose and Its Derivatives by Ister and Flegien which is incorporatedherein by reference.

In addition, for proofing applications, the nitrocellulose is preferablyadded in the form of nitrocellulose containing printing inks which arecompatible with the solvent used to dissolve the sensitizer. Examples ofsuch compositions include solvent based gravure inks.and processprinting inks.

As indicated above, the binder employed ideally is soluble in the samesolvent used for dissolving the near infrared absorbing sensitizer.However, dispersions may be used in appropriate circumstances when amutual solvent cannot be determined.

The coating composition may also contain other materials which arenon-absorbing at the desired laser emission wavelengths and/ornon-decomposing and do not adversely affect the absorbance of thetopcoat at the laser wavelength. These materials are selected dependingupon the function of the final product to be produced. These materialsmay play a role in the imaging chemistry or may be inert.

In a preferred embodiment, substances believed capable of donating H*(hydrogen atom) to the excited state of the sensitizer are included inthe coating compositions, and may thereby increase acid formation. Suchmaterials include alcohols, thiols, phenols, amines and hydrocarbons.Particularly preferred are low molecular weight secondary and tertiaryalcohols, diols and polyols such as 1,2-decanediol, pinacol,2,5-dimethylhexane-2,5-diol, 2,5-dimethyl-3-hexyne-2,5-diol andcombinations of these. Addition of the hydrogen atom donors to thecoating surprisingly enables the reduction of the amount of near IRabsorber(s) from about 50% by weight based on solids content to about 5%to about 15% by weight based on solids content.

However, if, for example, nitrocellulose is employed as the polymericbinder, the use of an additional hydrogen atom donor material is notrequired because the desired hydrogen donors are already present withinthe resin.

Other additives which may be included are selected dependent on thefinal application of the imaged product. These additives are materialswhich can be ablatively-transferred to a receptor element in apredetermined contrasting pattern of intelligence to visibly orsymbolically represent or describe an object or data, e.g., dyes andpigments, ultraviolet and infrared absorbing materials, polymericmaterials, magnetic materials, conducting materials, fluorescentmaterials, etc.

Still other additives may be included to enhance the film properties andtransfer characteristics. These additives need not function as acontrast imaging material and include, e.g., plasticizers, flowadditives, slip agents, light stabilizers, anti-static agents,surfactants, brighteners, anti-oxidants and others known to theformulation art.

In one embodiment of the invention, in which the imaging media can beeffectively employed in color transfer printing, the contrast additivesare visibly absorbing dyes or pigments. The particular choice isdictated by the specifications for the final colored print. For example,in a color proofing application suited to newspaper printing, AmericanNewspaper Publishers' Association (ANPA) specified Color Index (C.I.)Pigment Blue 15, C.I. Pigment Yellow 13 and C.I Red 57 are used with anewsprint receptor. For color imaging which need not conform to anyindustry specifications, visibly absorbing dyes such as those availablein the Morfast™ series (Morton International) can be used with anydesired receptor, e.g., office copy paper. By “color proofing” is ofcourse intended that technique, very well known to the recording art, ofpredicting or confirming one or more aspects of color printing prior topress, e.g., color rendition, tonal rendition, registration,composition, and the like.

In another embodiment, i.e., masking, in which the imaging media can beeffectively employed as an exposure mask for use in graphic arts orprinted circuit preproduction, the contrast additive comprises at leastone material, other than the black body absorbers known to the priorart, which is effective in blocking the light output from commonexposure devices. Exemplary such materials are curcumin, azoderivatives, oxadiazole derivatives, dicinnamalacetone derivatives,benzophenone derivatives, etc. By “masking” is intended that operation,also very well known to the recording art, including exposure of atypically light sensitive material, e.g., printing plate, resist, diazo,etc., through a pre-existing pattern of intelligence, e.g., a “mask”,which selectively blocks the exposure radiation according to the patternof intelligence, e.g., a printed circuit, newspaper page, etc.

In still another embodiment, in which the imaging media can beeffectively employed in a security printing application, the contrastadditives are substantially colorless materials which fluoresce in thevisible spectral region when exposed to ultraviolet light.Representative such materials include oxazole derivatives, oxadiazolederivatives, coumarin derivatives, carbostyryl derivatives, etc.

In yet another embodiment, the non-ablation sensitizing contrast imagingmaterial is magnetic, for the production of such machine readable itemsas information strips, checks, credit cards, etc. Exemplary thereof areiron, iron oxide, cobalt-iron oxide, barium ferrite, mixtures of theabove, and the like.

The sensitizer and ablative binder are present in amounts sufficient toallow rapid partial decomposition of the binder to gaseous andnon-gaseous products when the sensitizer interacts with imagingradiation, e.g., laser light. Preferably, the ablative binder is presentin an amount of about 20% to about 95% by weight of dry solids while thesensitizer is present in an amount of about 5% to about 50% by weight ofdry solids. In addition, the additives can be present in an amount ofabout 0.5% to about 50% by weight of dry solids while the hydrogen atomdonor, including that provided by the polymer itself, can be present inan amount of about 1% to about 10% by weight of dry solids.

To prepare the coating composition for depositing the topcoat accordingto the present invention, a solution or dispersion is formulated whichcontains solvent, the near infrared absorbing sensitizer, the ablativebinder and, optionally, the hydrogen atom donor and/or additives.Preferably, the components of the wet coating are present in amounts ofabout 0.2% to about 5% by weight of the absorbing sensitizer, about 0.5%to about 20% by weight of the ablative binder and, optionally, about0.5% to about 2% by weight of a hydrogen atom donor and/or about 2% toabout 20% by weight of the additives, with the remainder being solvent.

The dried coating is preferably less than three microns thick and mostpreferably less than one micron thick in order to minimize the amount ofenergy required for ablative transfer. Furthermore, the imaging mediumadvantageously has an absorption of at least 0.1 absorbance units at thewavelength(s) of the imaging radiation.

The solvent employed in the present invention includes those solventswhich dissolve both the binders and preferably the near IR sensitizers.Exemplary such solvents include water, chlorinated hydrocarbons, such asmethylene chloride, 1,1,1-trichlorethane, chloroform, carbontetrachloride, trichloromethane and the like; ketones such as acetone,methyl ethyl ketone, methyl propyl ketone and higher boiling analogswhose boiling points do not exceed the thermal decomposition thresholdsof the binder resin, or mixtures thereof.

After the solution or dispersion is formulated, it is coated onto thesupport substrate by methods which are well-known to this art such asMeyer rod coating, gravure coating, reverse roll coating, modified beadcoating or extrusion coating.

The support substrates employed can be either support films transparentto the imaging radiation or non-transparent such support films.Transparent support films which can be employed include glass,polyesters (by reason of their high optical clarity and dimensionalstability), polycarbonates, polyurethanes, polyolefins, polyamides,polysulfones, polystyrenes, cellulosics and any support substrate whichdoes not dissolve in the coating solvents employed, with polyestersbeing preferred. Examples of non-transparent supports include anynon-transparent support substrate which would not dissolve in thecoating solvents employed. These supports can include filled and/orcoated opaque polyesters, aluminum supports, such as used in printingplates, and silicon chips. The thickness of such support substrates isnot critical and can vary widely, same depending, for example, upon theparticular intended application and whether irradiated from the front orback surface thereof.

An anti-reflection layer (vis-a-vis the imaging radiation) mayoptionally be provided on the face surface of the support opposite theablative topcoat and/or on the receptor element, to enhance theefficiency of the ablative transfer by enabling more of the imagingradiation to be effectively utilized.

Such anti-reflection layer advantageously comprises one or morematerials which are recognized for this purpose in the recording art,for example those described in U.S. Pat. Nos. 3,793,022 and 4,769,306,and are also applied in known manner. Suitable materials, e.g., for apolyester support substrate having a refractive index of about 1.6, arecoatable materials having refractive indices of about 1.3 to 1.4.Exemplary such materials include Fluorad™ FC-721 from 3M Co., CaF₂,MgF₂, fluoropolymer, etc. The thickness of the anti-reflection layer(s)is selected as to provide the desired refractive properties for thelayer(s) with respect to the wavelengths of the imaging radiation. Forexample, where Fluorad™ FC-721 is employed as the anti-reflection layerand 1064 nm imaging radiation is used, a thickness of about 0.2 to 0.25microns is effective.

When the sensitizer is selected such as to be substantially colorless inthe visible spectral region (400-760 nm), the laser imaging materials ofthe present invention can be advantageously employed in a color imagingand proofing method. By this method, a receptor sheet is positioned andfirmly maintained, e.g., in a vacuum frame, relative to the abovedescribed laser imaging material in such manner that it is effective inreceiving materials which have been ablated from the imaging medium.

The material transfer phenomenon of the laser-induced ablation processis illustrated by the photomicrograph obtained by time resolved grazingincident microscopy, TRGIM, in FIG. 1.

FIG. 1 is a side view photomicrograph of an imaging medium according tothe invention and the illuminated space thereabove (in lieu of areceptor element), taken 100 nanoseconds after the initiation of a 260nanosecond pulse from a Nd:YAG laser, 4, directed through the polyestersupport, 3, about ¼″ from the edge thereof and into the absorbingablative topcoat, 2 (the imaging medium, per se, is more fully describedin the Example 6 which follows), to produce a plume, 5, of ablatedmaterials. The horizontal lines, 1, in the space above the medium areinterference lines resulting from the use of coherent probeillumination. The Nd:YAG laser (1064 nm output from a Quantronics116FL-0 laser controlled by an Anderson Laboratories' DLM-40-IR2.7acousto-optic modulator and a 40 MHz signal processor) delivered 0.6J/cm² in a 25 micron diameter beam (1/e²). In FIG. 1, both the laserexposed and unexposed areas of the imaging medium are shown.

FIG. 2 illustrates the use of an imaging radiation transparent supportsubstrate in the method of the present invention. In this embodiment,imaging radiation 4′ impinges upon the imaging material which comprisesan imaging radiation transparent support substrate, 1′, the ablativetopcoat, 2′, and a receptor element, 3′, from the back or support sideof said imaging medium.

FIG. 3 illustrates an alternative embodiment of the present inventionwherein the imaging material comprises a nontransparent supportsubstrate 5′. In this embodiment, the receptor element, 3′, is made ofimaging radiation transparent material and the imaging radiationimpinges upon the imaging material from the front or receiver sheet sideof the material.

In either embodiment, a pattern of imaging radiation at the desiredwavelength(s) is directed into the absorbing layer to effect rapidpartial decomposition of the binder(s) to gaseous products, etc., thatgives rise to that phenomenon of temporary pressure accumulationdiscussed earlier. This causes ablation of the topcoat and its transferto the receptor element, thus producing an imaged donor film, 6′, and acorresponding image of opposite sign on the receptor element, 7′.

The receptor element need not be specially treated or selected toeffectively receive materials from the donor medium and can include, forexample, those which are well-known in the art of proofing and printing,such as newsprint, coated or uncoated papers of all shades and color,opaque filled and opaque coated plastic sheets, with the printing stockto be employed in the particular color proofing application beingpreferred. Other suitable receptors include fabrics, wood, cardboard,glass, ceramics, leather, metals such as aluminum and copper, rubber,papers and plastics generally, etc. While the receptor element need notbe specially treated or selected to assist in the ablation-transferprocess, as indicated above, it is nonetheless also within the scope ofthis invention to employ a treated or coated receptor, for example areceptor sheet coated with an effective amount of an adhesive or sizing,to aid in the adhesion of the ablated topcoat thereto.

The imaging medium is most advantageously positioned and firmlymaintained in face-to-face registered direct contact with the particularreceptor element selected, to facilely transfer ablated topcoat thereto,by any means suitable for such purpose, e.g., positive pressure, avacuum, or even by the adhesive properties of the receptor elementitself.

In order to further illustrate the present invention and the advantagesassociated therewith, the following specific examples are given, itbeing understood that same are intended only as illustrative and innowise limitative.

EXAMPLE 1 Polyurethane Synthesis (Polymer VII from Table 1)

2,4-Toluene diisocyanate (TDI), 20 g, 2,5-dimethyl-3-hexyne-2,5-diol,16.3 g, dibutyltin dilaurate, 0.25 ml, and N-methyl pyrrolidone, 50 ml,were added to a 200 ml flask equipped with a magnetic stirring bar and anitrogen inlet. The solution was stirred 6 hours at 50° C., then at roomtemperature overnight. The polymer was isolated by precipitation fromwater. It had a molecular weight of approximately 7,000 (GPC) and athermal decomposition temperature of 165° C. (broad) as determined byDifferential Scanning Calorimetry (DSC) at a scan rate of 25° C./min.

The polyurethanes indicated by the Roman numerals V to XIII in Table 1were synthesized from the corresponding monomers depicted in the firsthorizontal and vertical columns by the immediately above procedure. Thepolycarbonates III and. IV in Table 1 were synthesized from thecorresponding monomers depicted, after appropriate derivatization of thediols as described in J. M. J. Frechet et al, Polymer Journal, 19(1),pp. 31-49 (1987):

TABLE 1

V VI III

VII VIII IV

IX X

XI XII

The above polymers were evaluated by DSC. The results reported in Table2 were obtained:

TABLE 2 MELT DECOMPO- SOFTENING/MELT ENERGY SITION POLYMER TEMP.(° C.)(J/g) TEMP.(° C.) III 139  22 180 IV 50 21 170 V — — 200 VI — — 110 VII46 85 165 VIII 100  — 113 IX — — 157 X 63 — 100 XI 94 22 206 XII 50 100 174 Ethyl 96 17 203 cellu- lose Poly- — — 171 acetal

EXAMPLE 2

The following solution was coated onto ICI Melinex 516 polyester film,12″×18″ and 4 mils thick, with a #4 Meyer rod at a loading of 0.5 g wetweight/ft². Addition of the components was in the order indicated:

 7.25 g Acetone 1.197 g Copolymer of 2,4-TDI & 2,5-dimethyl-3-hexyne-2,5-diol (Polymer VII from Table 1) 0.364 g Cyasorb IR 165 0.12 g 2,5-Dimethyl-3-hexyne-2,5-diol  1.06 g Morfast Yellow 101.

The yellow film thus produced was imaged in registration with anewsprint receptor using a yellow halftone separation film master on aCrosfield Datrax 765 Facsimile system which employed a Nd:YAG laser withoutput wavelength 1064 nm and an adjustable power output of 3-14 Wattsat the film plane. The Datrax 765 writer is commercial hardwareavailable from Crosfield Electronics Ltd., Milton Keynes, UK. Theimaging conditions for this experiment were adjusted to an output powerof 10 Watts which gave a fluence of 0.16 J/cm², an intensity of 2×10⁶Watts/cm² and an addressability of 1,000 lpi at a 1/e² spot diameter of25 microns. The yellow film was maintained in direct contact with thenewspaper receptor via vacuum hold down at a pressure of 20 inches Hg.An imaged yellow film (negative) and a registered yellow newsprint image(positive) were produced at a scan rate of 64 cm²/sec.

EXAMPLE 3

To make a two color print, the solution of Example 2 was prepared, butsubstituting a combination of Morfast Red 104, 0.76 g, and MorfastViolet 1001, 0.04 g, in place of the Morfast Yellow. The magenta filmthus produced was imaged as described in Example 2 using magentahalftone separation data with the yellow print from Example 2 as thereceptor sheet. A two color print (positive) and an imaged magenta film(negative) were produced.

EXAMPLE 4

To make a three color print, the solution of Example 2 was prepared, butsubstituting a combination of Morfast Blue 105, 0.4 g, and Morfast Blue100, 0.4 g, in place of the Morfast Yellow. The cyan film thus producedwas imaged as described in Example 2 using cyan halftone separation datawith the two color print from Example 3 as the receptor sheet. A threecolor print (positive) and an imaged cyan film (negative) were produced.

EXAMPLE 5

To make a four color print, the solution of Example 2 was prepared, butsubstituting a combination of Morfast Brown 100, 0.36 g, Morfast Blue105, 0.36 g, and Morfast Red, 0.36 g, in place of the Morfast Yellow.The neutral black film thus produced was imaged as described in Example2 using black halftone separation data with the three color print fromExample 4 as the receptor sheet. A four color print (positive) and animaged black film (negative) were produced.

EXAMPLE 6

The following formulation was coated as described in Examples 2 through5:

 7.25 g Acetone 0.364 g Cyasorb IR 165  2.5 g American Ink & CoatingsCo. gravure inks Process Yellow or Process Red or Process Blue orProcess Black.

The American Ink gravure inks included nitrocellulose. Films were imagedas described in Examples 2 through 5 to produce full color prints whichmeet ANPA specified solid ink hue and density on newsprint: cyan,0.90-0.95, magenta, 0.90-0.95, yellow, 0.85-0.90, black, 1.00-1.05.

EXAMPLE 7

The following solution was formulated and coated as described inExamples 2 through 5:

 7.25 g Acetone 1.197 g Copolymer of 4,4′-diphenyl methane diisocyanateand PARADIOL (trademark of Goodyear Chemicals) (Polymer X from Table 1)0.364 g Cyasorb IR 165  0.12 g 2,5-Dimethyl-3-hexyne-2,5-diol  2.5 gAmerican Ink & Coatings Co. gravure inks Process Yellow or Process Redor Process Blue or Process Black.

Films were imaged as described in Examples 2 through 5 to produce fullcolor prints, as well as individual imaged monocolor and black films.

EXAMPLE 8

To 8.35 g of a 50:50 mixture of 1,1,1-trichloroethane and methylenechloride were added 0.5 g of an alternating polycarbonate synthesizedfrom Bisphenol A and 2,5-dimethylhexane-2,5-diol (Polymer III from Table1); 0.1 g Cyasorb IR 165; 0.1 g 2,5-dimethyl-3-hexyne-2,5-diol; and 1.0g of any one of the Morfast colors described above. The solutions werecoated at a loading of 1 g of solution/sq.ft. with a #9 Meyer rod byhand drawdown. The dried films were imaged at 0.11 J/cm² versus the 0.16J/cm² in Example 2 on a Crosfield Datrax 765 to produce a color print ona receptor sheet and imaged monocolor or black films.

EXAMPLE 9

To 9.35 g of a 50:50 mixture of 1,1,1-trichloroethane and methylenechloride were added 0.5 g of an alternating polycarbonate prepared fromBisphenol A and 2,5-dimethyl-3-hexyne-2,5-diol (Polymer IV from Table1); 0.1 g Cyasorb IR 165; and 0.05 g of 2,5-dimethyl-3-hexyne-2,5-diol.The solution was coated on polyester film and imaged at 0.08 J/cm²versus the 0.11 J/cm² in Example 8 as described above to produce animaged light tan film and a reversal light tan image on a newsprintreceptor sheet.

By comparison, films prepared from bisphenol A polycarbonates,polyvinylidene chloride (Saran F120 or F300), polymethacrylonitrile,ethylcellulose N-7, or styrene/acrylonitrile copolymer as binders inplace of an ablative polycarbonate or polyurethane provided very littleor no image transfer to the receptor sheet at the imaging fluenceemployed in this example.

While this invention has been described in terms of various preferredembodiments, the skilled artisan will appreciate that variousmodifications, substitutions, omissions and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims including equivalents thereof.

What is claimed is:
 1. An organization adopted for transferring acontrasting pattern of intelligence from an ablation-transfer imagingmedium to a receptor element, consisting essentially of (1) anablation-transfer imaging medium including a support substrate and alaser radiation-ablative topcoat essentially coextensive therewith, saidessentially coextensive topcoat containing an effectingablative-transfer effecting amount of at least one non-black body,non-imaging sensitizer that absorbs laser radiation at a rate sufficientto effect the imagewise ablation mass transfer of said topcoat, and saidlaser radiation-ablative topcoat also containing an imaging amount of anon-black body, non-ablation sensitizing contrast imaging materialtherein, said non-black body, non-ablation sensitizing contrast imagingmaterial comprising a yellow dye or pigment a magenta dye or pigment, ora cyan dye or pigment, and (2) a receptor element in contiguousregistration therewith.
 2. The organization as defined by claim 1, thetopcoat of said ablation-transfer imaging medium comprising at least onelaser-ablative binder.
 3. The organization as defined by claim 2, saidat least one non-black body, non-imaging sensitizer comprising at leastone near infrared absorber/sensitizer.
 4. The organization as defined byclaim 2, said at least one non-black body, non-imaging sensitizer beingselected from the group consisting of a cyanine or phthalocyanine dye, ametal dithiolene, a methylene blue salt, a di- or triarylmethane cationsalt, a Wurster's blue salt or an onium salt.
 5. The organization asdefined by claim 2, said at least one laser-ablative binder comprising anitrocellulose, polycarbonate, polyurethane, polyester, polyorthoesteror polyacetal.
 6. The organization as defined by claim 5, said at leastone laser-ablative binder comprising a nitrocellulose.
 7. Theorganization as defined by claim 5, said at least one laser-ablativebinder comprising a polycarbonate.
 8. The organization as defined byclaim 5, said at least one laser-ablative binder comprising apolyurethane.
 9. The organization as defined by claim 2, said at leastone non-black body, non-imaging sensitizer being substantially colorlessin the visible spectral region.
 10. The organization as defined by claim2, said at least one laser-ablative binder comprising from about 20% to95% by weight of said essentially coextensive topcoat.
 11. Theorganization as defined by claim 10, said at least one non-black body,non-imaging sensitizer comprising from about 5% to 50% by weight of saidessentially coextensive topcoat.
 12. The organization as defined byclaim 1, said essentially coextensive topcoat comprising anablation-enhancing amount of at least one laser-ablative binderdecomposable by acid catalysis.
 13. The organization as defined by claim12, the essentially coextensive topcoat of said ablation-transferimaging medium further comprising an ablation-enhancing amount of atleast one hydrogen atom donor that promotes acid formation effecting theacid catalyzed decomposition of said at least one binder.
 14. Theorganization as defined by claim 13, said at least one hydrogen atomdonor comprising an alcohol, thiol, phenol, amine or hydrocarbon. 15.The organization as defined by claim 1, said at least one non-blackbody, non-imaging sensitizer initiating acid formation uponphoto-excitation thereof.
 16. The organization as defined by claim 1,the non-black body, non-ablation sensitizing contrast imaging materialof said ablation-transfer imaging medium comprising a yellow pigment, amagenta pigment or a cyan pigment.
 17. A system for transferring acontrasting pattern of intelligence from an ablation-transfer imagingmedium to a receptor element, comprising the organization as defined byclaim 11 and means for selectively irradiating one face surface of saidablation-transfer imaging medium with a beam of laser radiationcorresponding to said pattern of intelligence.